During this reporting period the Laboratory of Genetics and Physiology has initiated a program to study the role of cytokine-STAT5 signaling in the epigenetic programming of cells. As a test system we have analyzed mouse embryonic fibroblasts in the presence and absence of STAT5. We established the histone modification code for wild type cells as a basis for comparison of these marks in cells that lack one or both STAT5 proteins. Upon completion of the test program, we will expand into other cell types, whose biology greatly depends on cytokine signaling, such as mammary and hematopoietic cells.